Apparatus for treating pulverized fuel such as coal and the like



April 10, 1934- F. L. DoRNBRooK Er AL 1,954,351?

APPARATUS FOR TREATING PULVERIZED FUEL SUCH AS COAL AND THE LIKE FiledMaIQh 14, 1932 2 Sheets-Sheet 1 will 65 b j INV NT i -mef ATTORNEY.

April l0, 1934.

F. DoRNBRvooK Er AL '1,954,352

APPARATUS FOR TREATING PULVERIZED FEL'ASUCH AS COAL AND THE LIKE FiledMarch 14, 1932-. 2 Sheets-Sheet 2 nun"n"n"nUnn"nl'nlnlnununl]Iununununununununununununu ATTORNEY lnununununlnunununl'nun ,n

lILlLlUlIlllIU Patented Apr. 10, 1934 UNITED STATES PATENT OFFICEAPPARATUS FOR TREATIN G PULVERIZED FUEL SUCH AS COAL AND THE LIKEApplication March 14, 1932, Serial No. 598,796

Claims.

This invention relates to a new and improved apparatus for treatinghydrocarbon-containing fuels such as coal and the like in powdered form,including the step of Ylow temperature carbonization for the recovery ofcoal gas and other products resulting from carbonization and a powderedcoke fuel which may if desired, be fed directly to a combustion chamberwithout appreciable loss of heat from the carbonizing process and burnedwith highly satisfactory results.

The characterizing feature of this invention deals with an apparatus forthe treatment of powdered hydrocarbon-containing fuel such as coal,including an oxidation pre-treatment and llsubsequent low temperaturecarbonization and in addition, special provision in mechanicallyhandling and controlling the movement and condition of the fuel whilebeing subjected to the pre-oxidation and carbonizing treatments resulteingin the production of powdered coke and the elimination of alltendency to ycake or to in any wise clog the apparatus, and, for thefirst time, in a successful performance of this type of treatment.

Prior to this invention, low temperature distillation was known to bedesirable Vin many in-` stances, and numerous attempts have been made tosuccessfully perform low temperature carbonizat'ion with both lump andpowdered fuels. With the increasing use of powdered coal, it wasconsidered highly-desirable to endeavor to perfect an apparatus forcarbonizing powdered coal for the recovery of coal gas and otherproducts of distillation and with the aim of acquiring a powdered cokesuitable for use in ordinary pulverized fuel furnaces.

The difficulty, however, which prior to the present invention, hasblocked the successful developrnent of such apparatus flows from the 40tendency of coal to cake under the temperature and treatment necessaryfor a satisfactory carbonizing action which has not only destroyed thepossibility of recovering a powdered coke for fuel purposes but haswithout exception, caked in and clogged the apparatus to an extent whichrendered the undertaking entirely impractical and unsuccessful from thecommercial standpoint. It is this caking quality of coal thathas alsoprevented the development of a successful continuous treatment processof the type provided by this invention.

Among the methods and apparatus heretofore devised in an effort tosuccessfully carbonize powdered coal with a resulting powdered coke isincluded a pre-heating and/or oxidizing treat- (Cl. 21R- 108) ment andwhereas oxidation is known to free coal of its caking properties, theutilization of this known discovery has thus far baflled those skilledin the art insofar as the development of a commercial workable apparatusis concerned, which `would not suffer the defeat of ultimate cakingfailure.

Accordingly, it is an object of this invention to provide a new andimproved apparatus which nection, means may be provided by which the,

powdered coke is fed While still hot from the carbonizing retort into asuitable combustion chamber such as a furnace used for any desiredpurpose such as for instance, in heating steam boilers of a generatingplant or any other practical purpose.

It is a further object of this invention to provide an apparatus whichis highly satisfactory in performance and is well adapted to economicaland successful commercial installation whereby when used inconjunction'with a furnace, high efciency is realized both in thecombustion of the powdered coke and generation of heat and in therecovery of the desirable products of low temperature carbonization.

It is a furtherobject of this invention to provide an apparatus foraccomplishing the above stated objects which will utilize for treatment,powdered fuel such as coal or the like, and produce in addition to theby-prod'ucts of the carbonizing treatment, a coke fuel in powdered formwhich may be cooled and stored or lburned directly in its heatedcondition, but which in either case, may be satisfactorily handled andburned in combustion chambers now used for the combustion of powdered.coal.

As an advantage of this invention, the powdered coal and the resultingpowdered coke may be conveyed and transferred in enclosed pipes eitherby gravity or by currents or drafts of air or gases, so that the entireapparatus may comprise an enclosed system which makes for a high degreeof cleanliness and increased efcienoy and the avoidance of wastes andother losses incident to apparatus differing in this respect.

It is a further object of this invention to provide an apparatus inwhich pulverized, oxidized fuel is carbonized in a closed retort byheating with gases which are isolated from the space of the retortwhereby the gas recovered is not diluted or rendered of inferior gradeor lowered B. t. u. value, as would be occasioned when heating gases arebrought into direct association with the fuel in the carbonizing retort.

It is a further object of this invention when used in combination with acombustion space of a furnace to remove the hydrogen from the fuelduring the carbonizingy treatment, and to thereby enhance the heat valueof the resulting powdered coke by preventing the formation of watervapor during combustion and eliminating the consequent loss of heat ofvaporization to the stack. In the accomplishment of this object, most ofthe hydrogen passes off with the, gas in the carbonizing retort and doesnot enter the furnace, and it is found in practice, that the heat savedin this Way more than compensates for the losses due to radiation.

When the oxidizing and carbonizing apparatus is used in combination withthe combustion space of a furnace, it is a further object to providemeans for utilizing gaseous products of combustion taken from thecombustion space as a source of heat for conducting both the oxidizingand carbonizing treatments and in the oxidizing treatment means forutilizing such gaseous products of combustion as a conveying gaseousmedium for the powdered fuel. In this latter case the gas is ultimatelyreturned to the combustion space for vthe conservation of all fine fuelparticles which may remain suspended therein after the oxidized fuel hasbeen separated therefrom. In the accomplishment of this object thegaseous products of combustion during oxidation serve as an inertatmosphere containing only the desired and regulated quantity of oxygenfor proper oxidation of the entire mass with assurance againstcombustion during the oxidizing treatment.

One aspect of this invention is based upon a more thorough knowledge ofthe effect of preoxidation in the subsequent handling and condition ofthe coal in passing from the oxidizing apparatus to the carbonizer andthrough the carbonizer until the carbonizing rtreatment is completed.

The applicants have discovered that the results of an oxidizingtreatment upon a given mass of ordinary pulverized coal, for a likeperiod of exposure under the same conditions, differ widely insofar asthe caking properties are concerned, for particles of different size,that is to say; between the particles of maximum size as compared withthose of minimum size. A corresponding difference exists throughout theintermediate range of particle sizes. The period of oxidation treatment,temperature and other factors must be substantially the same for theentire mass as it is entirely impractical from the commercial standpointto subdivide the mass of powdered coal into numerous batches, each of aparticular size, and subject each bath to a different oxidizingtreatment, each designed and selected especially for properly oxidizingthe part there is no tendency to cake and the mass remains ticles of theparticular batch.

It is furthermore impractical from the commercial standpoint to subjectthe entire batch to a prolonged oxidizing treatment of length sucient tothoroughly oxidize the largest particles, on account of the fact thatsuch treatment will involve a temperature, quantity of oxygen, andtreatment period productive of combustion of the more minute particles.Inasmuch as an oxidation pre-treatment which would cause combustion ofthe more minute particles cannot be employed, the outstanding difficultyof processes heretofore devised and tried, insofar as the applicants,can determine, has been that of inadequate oxidation of the largerparticles, resulting in the subsequent caking of the larger particles toan extent that the apparatus employed was clogged with caked coke andthe process rendered inoperative.

Accordingly, the present invention contemplates an apparatus foraccomplishing an oxidizing treatment which is substantially the same forthe entire ymass so that it may be supposed if the applicants theory iscorrect, that some of the larger particles will be inadequately oxidizedbut with a handling of the entire mass in the oxidizer and in thecarbonizer in such a manner that the smaller oxidized particles serve asa coating for the larger, less oxidized particles whereby to irnpart tothe entire mass, the quality of behaving as a completely oxidized masswith the avoidanceA and entire elimination of caking tendencies duringthe carbonizing treatment.

As one aspect of the teaching of this invention, care should be taken toassure, during the grinding operation, the production of a sufcientlylarge proportion of smaller particle sizes so that under the subsequenthandling during oxidizing and carbonizing a treatment which may bereferred to as an average oxidizing treatment may be practised with theresult that the entire mass behaves as a completely oxidized mass. Ofcourse, it is understood that in no case should the oxidizing treatmentbe increased either by the amount of heat, quantity of oxygen ortreatment period, to the point where combustion will occur in theoxidizer.

According to the present invention the oxidizing treatment may beconducted in any suitable manner such as hereinafter outlined, providedhowever, that the apparatus is constructed so that after separation ofthe fuel particlesand the gaseous medium, the fuel particles are allowedto collect or settle as a static mass whereby the particles are at restand free from disturbing or yagitating forces or movements' such aswould operate to disassociate and separate the fine oxidized particlesfrom their coating association on larger particles.

Furthermore, the same conditions must prevail in the carbonizing retortan/d accordingly, this apparatus involves means for carbonizing the fuelWhile existing in the condition of a relatively static mass free fromdisturbing forces or movements which would cause exposure to each otherand to inner surfaces of the carbonizer of the larger partly oxidizedparticles. The movement of the mass through the carbonizer, essentialfor a continuous operation is accomplished by permitting the mass toslowly settle under the'action of gravity while the volatile material isbeing driven olf. Such movement does not disturb the condition of themass insofar as the ne coating on larger particles is concerned andconsequently entirely in powdered form whereby it is free to continueits slowly settling movement until it reaches the bottom where the fuelexists as coke dust. The coke dust can then be removed by any suitablemethod such as by means of a. conveyor and -as here disclosed, feddirectly into the combustion space of a furnace. j

In addition -to the above stated objects, this apparatus contemplatesvarious means which make for economy and commercial success and thesewill more readily appear to one skilled in the art. VAs the followingdescription proceeds, however, additional vadvantages may be mentionedas follows:

'I'his apparatus is well adapted for use in electric generating plantshaving steam boilers equipped for the handling and burning of pulverizedfuel and in such cases the apparatus may be conveniently placed betweenthe pulverized fuel bunker or similar source of supply and the inlet tothe combustion space without disturbing' -or seriously affecting thesteam boiler installation.

Accordingly, the valuable volatile constituents of the lcoal which wouldotherwise be burned in the steam generating boiler for their heat value,may by such an installation, be separated from the residual coke dustand recovered as coal gas, coal tar and oils. The advantage of so doingwill be appreciated when it is known that the com-- mercial value ofcoal gas, coal tar and the other by-products of coal distillation, isconsiderably in excess of their heating value. The present inventiontherefore is productive of the profit from the volatile products and atthe same time provides an adequate and satisfactory fuel in the form ofcoke dust for combustion in the furnace, the result of which is anincreased profit on the entire operation.

A further advantage is realized from the fact that the recoveredby-products are produced by low temperature distillation treatment whichis productive of a gas of great value and high in heating units. This isdue to the fact that a low distillation temperature does not expose thecoal gas tothermal decomposition or cracking such as might impair its`heating value per unit volume. The quality of the gas is also assured bythe avoidance of heating gases in direct contact with the fuel in thecarbonizer whereby only undiluted and clean products of distillation arerecovered. Other details of the process such as the filtering of the gasthrough the pulverized coal, the maintenance of the carbonizingtemperature, and so forth, assist in the production of clean gas and tarproducts withoutY danger of re-condensation in the carbonizing retort.

Likewise; tar of high value is produced by the low distillationtemperature because high destructive temperatures in the carbonizingretort are thus avoided. The products of distillation when removed fromthe retort, may be recovered by condensation of the tars and oils andthe collection of the gas in suitable containers, all in accordance withknown and satisfactory practice.

In the drawings, one form of apparatus is shown which has proven to behighly successful in practice and well adapted for large scalecommercial installation. i

` I'n order that the invention may be more readily understood, it willbe described in connection with the disclosed apparatus but it should beunderstood that the invention is not to be limited by this illustrativedescription as the scope thereof will be pointed out in the appendedclaims.

The apparatus of this invention may be considered .in connection withapplicants co-pending application Serial No. 525,940, filed March 28,

filed March 14th,'1932, which is a continuation in part thereof, andsome of the novel features relating to the treatment ofhydrocarbon-containing fuels shown and described but not specificallyclaimed herein form the subject matter of the before-mentionedco-pending applications.

In the drawings- Figure l is a side view, partly in vertical section ofa form of apparatus by which the present invention may be practised andas installed in connection with a boiler-furnace;

Figure 2 is an enlarged elevational view in cross-section of theoxidizer and separator shown in Figure 1; and

Figure 3 is an enlarged plan view in cross-section taken on the line 3-3of Figure 1 and looking in the direction of the arrows.

Construction of oxz'dz'eer and separator By referring to the drawings itwill be noted that the apparatus of this invention comprises a combinedoxidizer and separator, that is the pulverized coal is oxidized,separated and collected in a cylindrical container 60, which isconstructed in the general form of the usual cyclone separator.lindrical chamber 61 which serves as a vestibule space for thetangential introduction of pulverized coal to be treated. The coal isfed into the oxidizer through pipe 62 which is connected with anysuitable source of coal, such as an overhead bunker, hopper or ifdesired, directly with the pulverizing mill. The container is preferablycy,- lindrical in shape at its top portion and is provided with inclinedconical walls 63 at the bottom portion terminating in an outlet pipe 64.The outlet pipe leads directly to the carbonizer 65 as shown in thedrawings.

When this apparatus is used in connection with a furnace it ispreferable to use flue gases for the oxygen and heat carrying mediumwhich is fed into the oxidizer tangentially as at 66 through a pipe 67.By virtue of the tangential inlet, the gases are given a whirling motioninto which the coal falls from the vestibule chamber 61. the action ofthe centrifugal force the coal is thrown outwardly against the walls ofthe oxidizer but only after the particles thereof have been exposed tothe heating and oxidizing effect of the fiue gas. By virtue of thisaction, a. separation also occurs as the gases free from coal particlesare caused to occupy the central portion of the container where they arewithdrawn through an outlet pipe 68 which extends upwardly and thencedownwardly and connects with a suction fan 69.

In order that more accurate control over the oxidizing action may berealized, provision is made for re-circulating a desired amount ofthetreated coal after it has fallen and collected at the bottom of thecontainer for instance, as shown at '70. This means comprises an outletpipe 71 which connects with an intake of a fan '72 which fan dischargesupwardly through pipe '73 tanl Centrally of the top is a smaller cy- Dueto comprises two star wheels 74 and 75. Each wheel is designed to occupysubstantially the entire interior space of the outlet pipe whereby coalis fed to the carbonizing retort solely by rotation of the star wheels.To avoid leakage of coal gas past the seal a flue gas pressure equal toor slightly above the pressure in the carbonizer is maintained betweenthe star wheels. This is accomplished by connecting a pipe '74', betweenthe discharge of fan 69 and the space between the star wheels. Othermeans are possible for providing a gas-tight seal and for conveying coalfrom the oxidizer to the carbonizer.

As shown in Figure 1, iiue gas pipe 67 is in communication with flue gaspipes 7G and 77 respectively, both of which communicate with the fluegas passages from the furnace for withdrawing ue gases therefrom.

It will be noted, however, that these pipes take gases from differentportions of the iiue gas passages and consequently at differenttemperatures whereby a mixture of gas may be fed to the oxidizer byadjustment of valves '78 and '79 respectively, to supply any desiredtemperature. Valve 78 is located in the pipe 80, which extends from thepipe 77 to pipe 67 at a point above Valve 81. Pipe '77 also conveys fluegas to pipe 82 which is here shown as a downward extension of pipe 67and which ultimately leads to the heating elements in the carbonizer.Valve 81 serves to separate the upwardly flowing gas from the downwardlyflowing gas but by means of these valves and valve 83 located in pipe77, any desired temperature may be provided either in the oxidizer orthe carbonizer. In addition, pipe 67 is provided with an air bleed pipe84 prov`ded with a valve 85 by which additional air may be introducedinto the flue gas.

Operation of oxidizer and separator In operating this apparatus, thecoal is introduced centrally of the container as above described and theflue gas enters tangentially to establish a whirl'ng motion. The coalfalls downwardly from the vestibule space 61 and upon entering theoxidizer, the coal and flue gas are set in rotary motion whichthoroughly exposes the coal to the oxygen and the flue gas and causesoxidation to that degree which effectively destroys the caking propertyof the mass of coal. During the oxidizng treatment, the coal iscontinuously separated from the gas by centrifugal force as it is thrownoutwardly toward the walls of the oxidizer and the gas travels inwardlyand is discharged through the outlet pipe 68. The coal then moves by theaction of gravity down the inclined walls at the lower portion of thecontainer and collects at the bottom thereof for subsequent dischargeinto the retort. If greater oxidation is necessary, the re-circulatingfan 72 is put in operation whereupon any desired portion of the coal maybe again introduced at the top, and exposed a second time to theoxidizing treatment. This recirculation enables a wide variance n thedegree of oxidation as it is possible if found necessary, to adjust thecapacity of the re-circulating fan relative to the flow of coal throughthe oxidizer in a manner to assure re-circulation two, three or moretimes.

The re-circulation means has another important function which is that ofwithdrawing gas from the bottom of the separator which has been foundtoimprove the efficiency of the separator.

Furthermore, re-eirculation maintains more coal in the oxidizer and thusprovides an increased mass of coal furnishing heat which enables thereduction in the amount of heating flue gas required for thoroughoxidation. Reduction in the flue gas flow increases the time that coalis in the oxidizer and further improves theoxdizing action. Thisprinciple of separating the coal from the ue gases and re-circulating itis invaluable in reducing the size of the oxidizer and incidentallyminimizing surface heat losses. To increase the time element byincreasing the size of the oxidizer only works a hardship ifre-erculation is not practised.

The time that the coal is in the oxidizer is proportional to the timethat gas is also present, other conditions being equal. Therefore,re-circulating all the coal once, is equivalent to doubling the oxidizersize.

Published tests show that the rate of oxidation does not slacken untilafter the caking properties are destroyed. Therefore, having some coalparticles pass to the carbonizer with only one passage through theoxidizer, is not undesirable since other particles may re-circulate moretimes than the average and are oxidized proportionally.

This apparatus likewise provides a collected mass. At the end of theoxidizing action the minute particles will associate themselves with oraffix themselves to the larger particles and form a coating thereon andwhen collected as a mass at substantial rest in the base of the oxidizerand subsequently fed to the carbonizer, the desired conditions aremaintained for assuring non-cakingf properties in the mass as a whole.

Oxidz'zing treatment For successful destruction of the caking propertiesof coal, the following conditions must be satisfied:

l. Temperature must be adequate.

2. Time of treatment must be sufficient.

3. Enough oxygen must be present.

4. Oxygen must be brought into thorough contact with coal.

Temperature accelerates the process markedly. It is common knowledgethat weathering of coal reduces its caking properties. Yet years ofexposure are necessary to totally destroy caking of most coking coals.Most chemical reactions are doubled with each 10 C. increase oftemperature, which explains why the oxidizer described herein can beeiTective.

Temperature of the coal and flue gas mixture is normally regulatedslightly under the initial distillation temperature of the coalbeingprocessed. For most coals this temperature ranges between 500 and'700 F. The oxidation temperature employed may slightly exceed theinitial distillation temperature to deliberately sacrice by-preductyield in favor of more thorough oxidation. Since tests have shown thatoxidation decreases tar yield and increases gas yield, thoroughoxidation at high temperatures may be desirable in some cases.

With this invention the oxidizer serves as a preheaterfor thecarbonizer, efficiently heating the coal nearly to its distillationtemperature and i thus greatly reducing the size of the heating platesand the consumption of heat in the carbonizer. With the form ofapparatus described, any desirable temperature can be obtained in the'oxidizer by proper proportioning of the hot and cooler flue gases. Someheating occurs due to the oxidizing in the oxidizer which serves toreduce the amount of hot gases utilized. The active swirling of coal andgases serves to maintain uniform temperature in the oxidizer.

wardly to the feeder.

'Iime of contact between coal and oxygen as obtained in the cyclone typeof oxidizer is suificient for good results because the coal particlesmove relatively slowly to the walls and ,down- The coal is thusconcentrated, and the weight of coal in the oxidizer at any one timewill be considerably in'excess of the weight of flue vgas and coalwithout such concentration. This principle of concentrationgreatly'reduces the requisite size of the oxidizer. This concentrationof coal in the oxidizer is especially true of the finer particles, forthey travel most slowly to the walls. As above pointed out, experiencehas shown that the coarser particles of pulverized fuels cannotbeoxidized with practical success, and that only the nes need be oxidizedto prevent caking of the mixture. A type of oxidizer that would retainthe coarse particles at the expense of hurrying the fines would thus beless eicient. Non-caking fine particles surrounding or coating cakingcoarse particles prevent caking of the whole and allow maintenance ofthe mass in pulverized form throughout the carbonization process.

Preferential oxidation of simply the fines af fords attainment ofrelatively high tar yields if desired. It is known that oxidation ofcoal decreases tar yield, though with an increase of gas yield. Insituations Where tar is more. valuable than gas, this special feature ofobtaining noncaking properties by oxidizing only a fraction of the totalcoal, is valuable.

In some coals experiments show that, though oxidation increases gasyield at the expense of tar yield, the sum of heat units'in the twoproducts is reduced'. When tar and gas are equally valuable, it is thusdesirable to effect destruction of caking properties with minimumoxidation. Such is possible by the process of this invention.

By selecting larger oxldizers of the cyclone type or by increasing therecirculation of the coal,

the time which coarse and fine particles remain in the oxidizingatmosphere can be in, creased to obtain higher gas yield fromcarbonization. Increase of the ilue gas inlet pipe size reduces thewhirling velocity of the gas in the oxidizer and decreases thecentrifugal force causing slower coal movement to the walls and thusincreases the time of oxidation.

vThis invention contemplates the use of all types of oxidizers and`separators so long as they satisfy the above statedrequirements. It isimportant that no flat surfaces on which coal may collect be present andthat the separators have reasonably high efficiency so that too large apercentage of coal will not by-pass the carbonizer. Though the heatvalue of coal by-passing the carbonizer may be conserved in the furnace,high separation efiiciency is highly desirable because the mostthoroughly oxidized and most non-caking particles, the fines, areotherwise lost to the furnace.

' Proper ,oxidation temperatures will depend upon the caking propertiesofthe coal employed, the degree of oxidation desired to increase gasyield, and the amount of preheating wanted. The usual range is between500 degrees Fahr. and 700 degrees Fahr., ,thoughunusual conditions maydictate more or less. To reduce the oxidizer and carbonizer investmentcost, the use oftemperatures above which a small amount of volatilematter is lost, may be found desirable. The oxidizer is a much moreefficient heater than is the carbonizer, and the volatile lost is gener`ally largely water. No heat units are lost since the discharge is burnedin the furnace.

Oxidation with flue gas, as shown in this particular disclosure, isdesirable because its -high efficiency of oxidation permits completionof the '380 reactions with a less percentage of necessary Oxy/- gen thanin usual air. Fluegases prevent the possibility of explosion, since therate of spontaneous heating in low oxygen mixtures is too slow to causesudden increase of pressure. Hot flue gases are most readily obtained ina power plant, and in fact if their heat can be absorbed in otherequipment than existing boilers, economizers, or air heaters, overallplant efciency is increased. yThis invention contemplates re-circulationof flue gases which in itself is not ordinarily more efficient, butsince it reduces boiler duty, it does improve heat absorptionefficiency.

In cases where iiue gases and transport air do not contain sumcientoxygen, room air or pr'eheated air can be added as above described. Ifonly heated air ror other gases are needed, the plan does not precludetheir use. This type of oxidizer may be used with various 'types ofcarbonizers or one or more oxidizers may be used for each carbonizer,depending upon length of' the carbonizei bin and resulting levelling ofcoal above the carbonizer plates. Small separators are more efficientmechanically than large ones, though the latter cost less, occupy lessspace and suffer smaller heat losses.

Construction of carbonizer The carbonizer comprises a container 65,which is of substantially the same shape as that of the apparatuspreviously described in applicants copending applications, includingheating elements of substantially the same character but having specicmeans and mechanism for withdrawing the volatile gases distilled fromthe coal. 'Ihe upper portion of the container is provided with verticalwalls whereas the base thereof, has tapering walls 101 as shown inFigure 1.

At a point intermediate the height of the container are a plurality ofheating elements 102, spaced apart to provide slot-like spacestherebetween which heating elements are hollow and in generalconstructed as those previously described in said co-pendingapplications. They are preferably provided with internal partitions 103,providing a circuitous path for the heating gases passing therethrough.The heating gases enter each element through an inlet pipe 104 which aresupplied with hot flue gas from header 105 received from pipe 82, takenfrom the combustion 130 space of the furnace as previously described.

At the opposite side of the elements at the top, the gases are withdrawnthrough pipes 106 which lead to header 107 which is in communicationwith pipe 68, leading to the suction fan 69.

In addition, the heating elements may be provided with fins 120, whichproject laterally from the fiat plate surfaces thereof and which arepreferably formed of thin strips of steel'extending vertically and atright angles to the faces of 140 the heating plates. f

These Aplates may be placed at frequent intervals in order to assist theheat transfer efficiency.

In practice it is found that the heat transfer on the flue gas side ofthe plates is considerably 145 more favorable than that on the coal sideand thus extension of the surface on the coal side is desirable.

The fins constitute a means of reducing the distance through which heatmust be conveyed 15( ico through the coal. When constructed in themanner described, they project into the coal and contact coaly on bothsides and by being made thin, they serve as little or no obstacle to thedownward passage of the coal. The use of such fins improves theefficiency of the heater as it is found that the heat conduction throughthe ns is approximately 250`t'imes greater than heat conduction throughpulverized coal.

It will be noted that the suction fan 69 also withdraws gases from theoxidizer and carbonizer through pipe 68 and that thereafter all of thegas is discharged through pipe 108 to a header 109, and thence throughpipe 110 into the coke dust feed pipe 111. Coke dust feed pipe 111discharges directly into the combustion space of the furnace whereby thecoke dust is burned as the heating fuel. The coke dust is extracted fromthe bottom of the carbonizing container by any suitable means such as ascrew conveyor 112, actuated by a pulley 113 rotated from any suitablesource of power (not shown). A super-heater may be provided comprisingone or more hot gas pipes 114, extending through the upper portion ofthe space in the carbonizer and connecting with the flue gas pipe 82 attheir inlet ends and nue gas pipe 68 at their discharge ends, wherebyhot flue gases maybe circulated therethrough at a temperaturesubstantially equal to that of gas entering the heating elements of thecarbonizer. This may or may not be employed as described, but itsfunction is that of preventing the condensation of tar and oils on thecarbonizer walls above the coal space and incidentally exerting acracking action if desired, on the volatile gases of distillation forpurposes hereinafter described.

The gases of distillation are taken off of the top through an outletpipe 115 leading to a header 116 which conveys the gases to suitablecleaning and condensing apparatus (not shown) after which the separatedconstituents may be recovyered and stored in the usual way.

It is important to observe that the carbonizing container is adaptedtobe kept constantly filled with oxidized, pulverized coal up to a pointsubstantially as represented by the line 117 in Figure 1. As previouslymentioned in connection with the collecting operation, the pulverizedcoal is thus allowed to accumulate as a mass which is free fromdisturbing forces or movements, such as would tend to separate the fineand large particles. To characterize this condition of the coal it isherein referred to as a static mass although it is to be understood thatthe mass is free to settle downwardly by the action of gravity as itundergoes carbonization.

The plate-like heating elements are disposed vertically so as to permitthe free passage of the coal downwardly at av rate determined by therate of extraction from the bottom by the screw conveyor 112. Animportant aspect of the apparatus is that the oxidized, pulverized coalexists in the form of a mass when exposed to the carbonizing treatmentwhereby all tendency to cake is eliminated.

By virtue of this treatment, the coal, after oxidation in the abovedescribed manner, behaves as a completely oxidized mass and therebycontinues to exist in pulverized form and passes downwardly through thecarbonizer Without caking and is finally extracted in the form of a cokedust.

Under thev influence of the screw conveyor, the coke dust is readily fedthrough the fuel inlet 111, into the combustion space of the furnace, It

is not essential to this invention to introduce the returned iiue gasesinto the inlet pipe 111, as is here shown, but this is found to assistin the conveying action and to cause the fuel to bev supplied in thecombustion space in a desirable manner.

By returning the flue gases all of the fuel particles which may haveremained suspended in the gases withdrawn from the oxidizer, arereturned to the furnace with the consequent saving of their heat value.

Operation of carbonizer In operation, when the coal treating apparatusof this invention is used in connection with a furnace, the carbonizingcontainer may be an existing structure or it may be built especially forthe process. It is possible to use containers interchangeably foruntreated and oxidized coal because by proper manipulation the changefrom one kind of coal to the other may be made without interfering withthe boiler operation.

If the carbonizer is operating and coke is being fed to the furnace thechange to the feeding of untreated coal may be made by gradually coolingthe carbonizer plates, and then shutting off the supply of oxidized coalto the container and turning on the supply of untreated coal. If thecarbonizer is not operating and untreated coal is being fed to thefurnace the change to feeding coke dust may be made by turning on thesupply of oxidized coal and when the untreated coal in the container hasreached a level below the carbonizer heating elements, the hot fluegases may be turned on and the carbonizer heated to operatingtemperature. Slow variation of coal temperatures leaving the oxidizerand elimination of heat from the carbonizer plates can afford any degreeof coal temperature to facilitate the changing of operations. The solerequirements of the container consist of sufficient size forinstallation of adequate heating surfaces and of its proper design toallow fairly uniform flow past these heating surfaces. Need ofinsulation is obvious.

The heating surfaces in the carbonizer may take any form commensuratewith their efficient performance, reasonable cost, and propermaintenance. As shown in Figures 1 and 3, plates of envelope shapethrough which the heating gases maypass are preferable, but tubes orother types of heating surfaces may be employed. Carbon steel, stainlesssteel, calorized carbon steel, or other materials resistant todeterioration by high temperatures maybe employed. Carbon steel allowsheating the coke dust to a temperature of 1,000 degrees F., and othermetals, if used, may extend the limit to 1,500 degrees F.

Efficient heat transfer is the most important requirement of theseheating surfaces. Short distance of heat travel from the heatingsurfaces to the center of coal strata heated is of major importance,since pulverized coal is a very poor conductor of heat. Approximatecounterow of flue gas and coal is likewise important for maximumefficiency. The heating surfaces should not cause undue restriction tothe downward ow of coal, and preferably should displace a minimum volumeof coal in the container so that a maximum time of contact for heatingmay occur. In present average power plant practice, coal falls inpulverized fuel containers at the rate of about one foot per hour.Making the heating surfaces high and of small displacement of volumeaffords long time of contact.

Since the sustained strength of steels at high temperature is very low,it is important that the heating surfaces be of efficient design fromthe strength standpoint. Each element of the surfaces should have a highsection modulus when considered as a horizontal beam so that maxir mumstresses causing sagging may be below the b widely and 'causes inefcienttransfer.

reasonable creep limit of the material employed. Oxidation of the steelis low because of low oxygen content in the flue-gas and coal gas.

Applying fins on the plate-type surfaces as above* described is moreefficient than applying them to tubes because in the former case allfins are parallel and the distance of heat transfer through the layersof coal is uniform. When used on tubes radially this same distancevaries Since strength of these fins is not important they may be made ofless expensive material than the heating platesv-r Slow heating of coalin the carbonizer is a special feature reducing possibility of caking.It is generally known that rapidity of heating increases the degree ofcaking. In the usual case Where plates four feet high are\employed ap'-proximately four hours continual, uniform heat-A ing is required tocarbonize coal.

Continual motion throughout the carbonizing process further reducestendency` of caking.

Upward passage of coal gas through the coal being carbonized is afurther means vof insuring non-caking and uniform coal flow between theheating plates. This upward gas flowv prevents mechanical packing of thecoal and causes a continual maintenance of a very fluid, low` densitymixture of coal gas and coal. Thoroughly aerated pulverized coal weighsapproximately 35 pounds per cubic foot, yet tamping of the containerholding this coal allows reduction of the specic volume to the pointthat 55' ,pounds per cubic foot density occurs. When packed to thislatter density, the coal is almost self-supporting in a vertical pipeand its downwardl flow is not dependable. However, an aerated coalweighing 35 pounds per cubic foot resembles water in its fluidity. Thisfeature of maintaining the pulverized coal in an aerated statethroughout its flow between the heating plates is very important towardssuccess of the process.

In addition to the above results obtained by reason of the upwardpassage of coalgas through the coal being carbonized, it has been, foundthat this action is important in attainment of effective heating of thecoal mass. The coal gas passlng upwardlyA therethrough carries with itconsiderable heat, and the heat so carried serves to heat the coal sothat the coal is heated more effectively than it would be if heatedmerely by conduction alone from the envelope-like heating elements.

Coal dust separation from the coal gas occurs by subsidence, for theupward velocity of the coal gas is extremely low. .If the oxidized coalis introduced in the carbonizer without undue dust disturbanceexperienceshows that coal gas drawn from thetop of the coal container isexceedingly clean.

If tar of maximum quantity and value is desired it will be obtained fromthis design, since immediately upon distillation of the coal it entersregions of no higher temperature. There is no cracking of the tar toinferior products. Though it is retained in the coal gas space above thecoal for some appreciable period of time,

cracking at this point is minimum because of the temperature existingthere, 'unless the superheater is used for cracking purposes asdescribed later.

High B. t. u. gas ris obtained'from the/ process because there is littleor no dilution by the heating flue g s and because 'there is no crackingto deteriorate the heating value.

If it is desired to obtain a high gas yield at the expense of the taryield, super-heating surfaces can be installed in the coal gas space atthe top of the container for the purpose of crackingpart of the tarvapors to gas. Tests have shown that exposure of these tarvapors to atemperat'ure of 1300 degrees F. foran Aappreciable period of time mayhalve tar yield and double gas yield. The time element is important' forthis tar cracking and utilization ofthe large space in the top of thecarbonizing container is desirable from this standpoint. Thesesuperheating surfaces will also have the m'erit of preventingcondensation ofthe tars on walls or the top of the container especiallylwhen starting and stopping.

V If the carbonizer discharges coke dust too hot fuel-treatmentapparatus including the oxidizer and carbonizer Will be realized insofaras the production of the distilled gases and powdered coke is concernedwhen not used with a furnace. 'I'he apparatus is merely one which ispeculiarly adapted with greater advantage for use with a furnace.

What is claimed is: i

1. In an, apparatus for treating pulverized fuel, acasing forming anoxidizing chamber, and a concentric fuel admission chamber of lesserdiameter located at one end of the oxidizing chamber, means forintroducing oxygencontaining heating gas tangentially into saidoxidizing /chamber from the periphery-thereof to produce a vortex of gaswithin and advancing along said chamber, means for introducing pul-Verized fuel tangentially into said fuel admission chamber to produce asimilarly swirling vortex advancing along said oxidizing chamber withinthe gas vortex vto cause the particles of fuel to move outwardly throughthe gas, and' means .for withdrawing the gas from said oxidizing chambernear the center of the vortex and remote from said gas and fuelintroducing means. f

2. In an apparatus for treating pulverized fuel, a casing forming anoxidizing chamber, and a concentric fuel admission chamber of lesserdiameter located at one end of the oxidizingv chamber, Imeans forintroducing oxygen-containing heating gas tangentially into said oxidiz-CII move outwardly through the gas, means for withdrawing the gas fromsaid oxidizing chamber near the center of the vortex and remote fromsaid gas and fuel introducing means, and means for removing treated fuelfrom the lower portion of said oxidizing chamber remote from the zone ofsaid vortices.

3. A combined oxidizing and carbonizing unit for pulverized fuelcomprising an oxidizer, a superimposed fuel entrance chamber centrallyat the top thereof, means for introducing fuel into said entrancechamber, means for introducing oxygen-containing, heating Agas into theupper portion of the oxidizer from the periphery thereof to produce avortex of gas within the chamber, means for introducing pulverized fuelinto said entrance chamber and into said vortex near the center of theoxidizer to cause the fuel particles to move outwardly through the gas,means forming a carbonizing chamber disposed adjacent said oxidizingchamber so as to receive the oxidized fuel from the lower portion ofsaid oxidizing chamber and having a lower fuel outlet, means within saidcarbonizing chamber for nally carbonzing the fuel passing therethrough,and means for conducting the oxidizing gas from said oxidizing chamberto the fuel outlet from Said carbonizing chamber.

4. A combined oxidizing and carbonizing unit for pulverized fuelcomprising an oxidizer, a superimposed fuel entrance chamber centrallyat the top thereof, means for introducing fuel into said entrancechamber, means for introducing oxygen-containing, heating gas into theupper portion of the oxidizer from the periphery thereof to produce avortex of gas within the chamber, means for introducing pulverized fuelinto said entrance chamber and into said vortex near the center of theoxidizer to cause the fuel particles to move outwardly through the gas,means forming a carbonizing chamber disposed adjacent said oxidizingchamber so as to receive the oxidized fuel from the lower portion ofsaid oxidizing chamber and having a lower fuel outlet, means forwithdrawing desired amounts of treated fuel from said oxidizer andre-introducing it into said oxidizer for re-treat-ment, means Withinsaid carbonizing chamber for nally carbonizing the fuel passingtherethrough, and means for conducting the oxidizing gas from saidoxidizing chamber to the fuel outlet from said carbonizing chamber.

5. A combined oxidizing and carbonizing unit for pulverized fuelcomprising, means forming an oxidizing chamber having a fuel inlet and aheating and oxygen-containing, heating gas inlet, a carbonizer disposedadjacent said oxidizing chamber so as to receive the oxidized fucltherefrom and having a lower fuel outlet, said carbonizer comprising aretort adapted to contain a collected mass of fuel received from theoxidizing chamber and adapted to have said mass of fuel descend slowlyby the action of gravity, enclosed heating elements disposedintermediate the height of the retort, said heating elements beingspaced and relatively thin so that the free downward passage of saidfuel therebetween and the transfer of heat relatively uniformlythroughout the entire mass of fuel Within the region of said heatingelements is accomplished, with the upward passage of coal gas throughthe fine fuel mass, whereby the fuel mass will absorb heat from saidupwardly passing gas, and means for conducting the oxidizing gas fromsaid oxidizing chamber to the fuel outlet from said carbonizing retort.

FREDERICK L. DORNBROOK. MONTROSE K. DREWRY.

